Abstract
This paper presents edge measurements utilizing Langmuir probes to characterize plasma turbulence in the Helically Symmetric Experiment (HSX) [F. S. B. Anderson et al., Fusion Technol. 27, 273 (1995)]. Normalized density and potential fluctuations exhibit strong intensities but are comparable to mixing length estimates using measured correlation lengths. The correlation lengths are isotropic with respect to radial and poloidal directions and follow local (gyro-Bohm) drift wave expectations. These observations are common to measurements in both the optimized quasihelically symmetric (QHS) configuration, as well as a configuration where the symmetry is degraded intentionally. The resulting turbulent particle flux in higher density QHS discharges is in good quantitative agreement with transport analysis using three-dimensional neutral gas simulations. The measured turbulence characteristics are compared to a quasilinear trapped electron mode (TEM) drift wave model [H. Nordman, J. Weiland, and A. Jarmen, Nucl. Fusion 30, 983 (1990)] that has been used to predict the anomalous transport in HSX. While quantitative differences exist (factors of 2-3), there is a general consistency between the turbulence measurements and the TEM drift wave model.